A known projector which controls an associated illumination device by using a light shield unit has a pair of light shield members rotated to open and close, for example, as components disposed in such a position as to be symmetric with each other with an illumination optical axis interposed therebetween, and positioned between a pair of lens arrays within the illumination device so as to control the shield amount of illumination light by using the light shield members (for example, see JP-A-2007-71913 and JP-A-2004-69966). According to a known structure, the light shield members are constituted by block-shaped light shield bodies which have notch-shaped recesses to control the change of the light shield amount (see JP-A-2005-17501).
However, when the light shield is achieved by the opening and closing operation of the plate-shaped light shield members (light shield plates) as disclosed in JP-A-2007-71913 and JP-A-2004-69966, for example, there is a possibility that the change of the light shield amount does not become smooth. Moreover, when the block-shaped light shield bodies having the notch-shaped recesses are used as the light shield members as proposed in JP-A-2005-17501, the light shield bodies need complicated curved surfaces to produce a desirable change of the light shield amount in some cases, which may increase the space occupied by the light shield bodies.